Conventionally, a motor having a structure where a rotor is loaded with a permanent magnet is known. Since the motor with the above described structure is efficient, less easily damaged and may have large output, the motor with a permanent magnet is widely used. In the above described permanent magnet-type motor, generation of “cogging torque” is inevitable. For example, a motor with a large cogging torque, when rotated at high speed, produces vibration and noises.